WO 2010/151798 describes the addition of aliphatic polyesters such as polybutylene succinate (PBS) and polybutylene succinate-co-adipate (PBSA) in order to reduce the aerobic biodegradability of polyhydroxyalkanoate articles. The anaerobic digestion of the abovementioned polymer mixtures is not mentioned in WO 2010/151798.
Under anaerobic conditions, aliphatic polyesters such as PBS, polybutylene succinate-co-sebacate (PBSSe) and PBSA are not degraded. Polyhydroxyalkanoates (PHA), in contrast, are degraded under anaerobic conditions. In analogy to the results found in WO 2010/151798, it is to be expected that, in a compound consisting of components a) and b), no more than component a) (PHA) will be degraded, while component b) remains. With b) in the continuous phase, it can even be expected that the degradation of the disperse PHA phase will be significantly disrupted or even inhibited.
US 2004/025552269 describes the anaerobic digestion of polymer mixtures comprising 15% by weight of polybutylene succinate-co-adipate and a mixture of various polyhydroxyalkanoates. The digestion rates after 28 days are 30% lower than the digestion rate of mixtures comprising exclusively polyhydroxyalkanoates. Under the conditions specified in US 2004/025552269, the polybutylene succinate-co-adipate is apparently not digested; there is accordingly no complete anaerobic digestion of the polymer mixture.
In the biological treatment of organic wastes, the process of anaerobic fermentation is becoming more important.
In contrast to biodegradation under aerobic conditions, in which CO2 forms as the terminal metabolic product, biodegradation under anaerobic conditions leads not only to CO2 but additionally to CH4 as a metabolic end product, which is utilizable for energy purposes. The mixture of carbon dioxide, methane and traces of further gases which is formed in the course of anaerobic fermentation is called biogas.
By virtue of the energy recovery, the process of anaerobic fermentation, optionally coupled with subsequent aerobic composting, has advantages over purely aerobic composting (cold combustion).
The polyhydroxyalkanoates generally have low melt strength and—closely connected to this—low strain viscosity/strain hardening. They can therefore be processed further to films only with difficulty in standard production processes, for example film blowing.